The transmission of carrier signal in power line transporting electric energy has the problem of seriously mismatched impedance. Therefore, it is impossible to design larger output power of carrier communication equipment, and the carrier signal power actually transmitted in power line is very weak. The interference noise and pulse in power line come from high-power electric equipments in power line distribution network, and these equipments are randomly “on” or “off” through high-voltage switches. Therefore, the power is very high. The power difference of these two strong and weak signals can reach up to over 50 dB. Even though the mixed superposition of two signals in power line is based on strong interference noise on indicators of frequency and amplitude, the weak carrier signal can slightly change the amplitude of strong interference noise through superposition. However, it will be a very difficult job to directly separate and measure it through dedicated circuits or instruments. Although the strongly interfered carrier signal actually transmitted in power line is very complicated, and is impossible to be predicted or difficult to be specifically described with a stable signal, in consideration of principle that any complicated signal can be decomposed into a variety of sine wave signals with different frequencies and different amplitudes according to Fourier transformation, we can simplify the carrier signal actually transmitted in power line and damaged by strong interference noise or pulse into the superposition of two lists of sine wave signals with amplitude difference of 50 dB and different frequencies. After the superposition, the signal frequency and amplitude are based on strong sine wave signals, and the weak sine wave signals add their own information through slightly changing the amplitudes of strong sine waves by superposition. The following description of two waveforms of superposition can be equivalent to waveforms of all carrier signals damaged by strong interference noise in power line.
The first superposition waveform appears when the strong sine wave frequency is lower than weak sine wave frequency, which can be described as: in a period of strong sine wave, its amplitude slightly changes with the amplitude change of weak sine wave in various periods. The weak change of this strong sine wave amplitude carries the information of weak sine wave signal.
The second superposition waveform appears when the strong sine wave frequency is higher than weak sine wave frequency, which can be described as: the strong sine wave amplitudes of various periods slightly change within a weak signal period, carrying the information of weak sine wave signal through this change. We can easily see the description of waveforms of these two signals, which although come from the same principle of waveform superposition, however the waveform structures are essentially different. If we design a suppression sine wave circuit, which can effectively suppress the strong sine wave signal of which the frequency is lower than weak sine wave, and improve the weak sine wave signal with higher frequency. However, when swapping frequencies of strong and weak sine waveforms, the strong sine wave signal is improved and enhanced on the contrary, and the weak sine wave signal is suppressed, thereby getting the opposite results. Thus, the above noise suppression method has strict prerequisite conditions.
Therefore, the mutual frequency range of strong and weak sine waves in channel shall be effectively, accurately, and randomly distinguished and completed with time-sharing processing. The strong and weak represent the interference noise and communication signal, so as to effectively suppress the strong sine wave signal in the whole channel, which is the key on improving the signal to noise ratio.
As mentioned above, due to the amplitude difference of both strong and weak sine waves of 50 dB, the frequencies of strong and weak sine waves shall be determined in advantage for distinguishment of mutual frequency scope, and then the noise suppression method shall be selected, which can't be achieved in circuit design of existing technology. Therefore, another more practical and effective mode shall be found to distinguish randomly changed noise frequencies and automatically transmit them to applicable processing channels. This is the technical problem that needs to be resolved by this invention.